The present invention relates to a fan comprising a hub that rotates and a plurality of blades attached to the hub in a radial pattern around said hub, as well as a personal computer equipped with the fan.
Personal computers (PC) and, in particular, notebook PCs, have seen dramatic increases in CPU speed and performance while becoming smaller in size and lighter in weight that their predecessors. As a result, the heat diffusion in modern machines also has become increasingly important. A ventilation fan is critical element in heat diffusion that is found in almost every PC and is a core element of the cooling system in PCs.
FIG. 7 shows how a fan is installed in a conventional notebook PC. FIG. 8 shows the positional relationship between the fan and the cover of the PC. In FIGS. 7 and 8, the fan 51 is of a flat type comprising a rotatable hub 53 and a plurality of blades 54 attached to hub 53 which is fixed to the rotary shaft of a motor (not shown) in the fan body 52. The blades 54 are disposed around the hub 53 in a radial pattern. The fan 51 is disposed between a cover 61 and a keyboard 62, closer to an inner surface of cover 61. In addition to the fan 51, a board 63 is also disposed between cover 61 and keyboard 62. Various elements such as a CPU 64, etc., are mounted on board 63. In FIGS. 7 and 8, blades 54 of fan 51 are rotated to pull the air between cover 61 and keyboard 62 inside the PC into fan 51 from its lower side. The air is then discharged out of the PC through vent holes 65 provided in the cover 61 at the side of the fan 51 to reduce the operating temperature of the PC.
In order to release the heat from the interior of the notebook PC with fan 51, it preferable to increase the air flow rate of fan 51. An effective way to increase the airflow rate of fan 51 is remove resistance of the air flow inside the PC, or increase the rotational speed or the number of blades of the fan. For very thin, lightweight notebook PCs, the clearance between board 63 and cover 61 must be minimized. Unfortunately, such a configuration significantly increases the resistance of the air flow and makes it virtually impossible to reduce the path of the air even slightly so as to increase the air flow rate in conventional notebook PCs.
However, when the air flow rate is increased by increasing the rotational speed and number of blades of the fan, an unpleasant and, thus, unacceptable increase in noise level is created. Thus, the rotational speed, number of blades, and the noise level of the fan are related proportionally to each other. Typically, noise generated by fan blades has a peak frequency in a range calculated by the following equation:
xe2x80x83Peak frequency (Hz)=number of bladesxc3x97rotational speed (rpm)/60
For example, a fan having seven blades rotating at 5200 rpm in a conventional notebook PC has a peak frequency of about 600 Hz. If the number of blades is increased to nine, the peak frequency will be about 780 Hz at the same rotational speed. This equation also holds true when the rotational speed is increased above 5200 rpm while the fan has the same number of blades. However, if the peak frequency is too high, the microphone of the PC picks up the noise and disables the function. With respect to these problems experienced with conventional fans, it is an object of the present invention to provide a fan that can increase the air flow rate while keeping the noise level within a permissible range, as well as equipping a PC with such a fan.
The present invention is directed to a fan having a plurality of blades disposed around a hub that rotates, and preferably to a fan employable for a PC (Personal Computer). Each of the blades of the fan is shaped differently from the others to an extent that the air volume handling capacity of the blades is not substantially diminished. The present invention is also directed to a PC that employs such a fan as a cooling or ventilation fan.
The noise level generated by a fan in a specific frequency range is caused by the change in air pressure and is attributable to the symmetry fan blade shape. By altering the shape of the individual blades, the noise level due to the pressure changes is attenuated. Each blade of the fan slightly differs in shape from the others to eliminate the periodic occurrence of air pressure changes. The noise level of the fan is suppressed within an allowable range even when the number of blades and the rotational speed of the fan are increased so as to increase the air flow rate.
In a preferred embodiment of the present invention, the shape of each blade is varied from the others by putting an adhesive, preferably putty, on the front surface and/or the back surface thereof near the hub. In addition, by putting an adhesive or putty on the front surface and/or the back surface of the blade entirely, the shape of the blade is varied from the others. In addition, the adhesive is put on every other blade. When the fan has an odd number of blades, the adhesive blades and non-adhesive blades are disposed adjacent to one another. The fan may also be provided with nine blades and rotate at a speed in excess or 5200 rpm. The present invention can thus be achieved in a preferred manner in any of the above cases.